Problem: Daniel is 78 years old and Luis is 9 years old. How many years will it take until Daniel is only 4 times as old as Luis?
Answer: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Daniel will be $78 + y$ years old and Luis will be $9 + y$ years old. At that time, Daniel will be 4 times as old as Luis. Writing this information as an equation, we get: $78 + y = 4 (9 + y)$ Simplifying the right side of this equation, we get: $78 + y = 36 + 4 y$ Solving for $y$ , we get: $3 y = 42$ $y = 14$.